Zion is such a great adventure.  If you drive the Zion-Mt. Carmel Highway, about 6 miles from the Visitor Center, you will find the Tunnel.  It is about 1.1 miles long, and when it was completed in 1930, it was the longest tunnel of its type in the United States.  It is a dark and spooky drive with a few openings along the way that let in some light and some views of the mountains.  Beyond the Tunnel is a completely different section of the Park with some great hiking spots to explore.